Method for local reversible glass swelling

ABSTRACT

A method of forming, on the surface of a glass material, a raised feature having a height within a target range, comprising ( 1 ) providing a glass material having a surface, ( 2 ) providing the glass material locally, at a location at or below the surface, with an amount of energy causing local expansion of the glass material so as to raise a feature on the surface at the location, ( 3 ) detecting the height of the raised feature or the height over time of the raised feature, ( 4 ) ( a ) if the height is below or approaching a value below the target range, providing the glass material at the location with energy in a greater amount, or ( b ) if the height is above or approaching a value above the target range, providing the glass material at the location with energy in a lesser amount, and ( 5 ) repeating steps ( 3 ) and ( 4 ) as needed to bring the height within the target range. Methods and devices for automating this process are also disclosed.

This invention was made with Government support under Agreement No.H98230-05-C-0429 awarded by Maryland Procurement. The U.S. Governmenthas certain rights in this invention.

BACKGROUND

This invention relates to surface texturing of glass materials andspecifically to surface texturing of glass materials induced by locallyapplied energy. Such texturing may include making bumps, ridges, and allvariety of more complex surface features resulting from combinations ofthese.

The effect of glass swelling when locally irradiated with a laser isknown. Small bumps, less than a few micrometers, formed by heating aglass surface with a CO₂ laser, have been reported, such as in U.S. Pat.No. 5,567,484, “Process for Texturing Brittle Nonmetallic Surfaces”(1996). Raising larger bumps into shapes defined by an overlying moldhas also been reported, such as in U.S. Pat. No. 7,152,434, “Method forProducing Planar Lens and Planar Lens Array” (2006). It would bedesirable to be able to raise bumps on a glass surface to significantheights, such as beyond a few micrometers or even as great as 100micrometers or more, but with fine reproducibility and control of theheight such as control as tight as ±100 nanometers, without beinglimited to the form or shape of a particular mold surface.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, the invention includesa method of forming, on the surface of a glass material, a raisedfeature having a height within a target range. The method comprises (1)providing a glass material having a surface, (2) providing the glassmaterial locally, at a location at or below the surface, with an amountof energy causing local expansion of the glass material so as to raise afeature on the surface at the location, (3) detecting the height of theraised feature or the height over time of the raised feature, (4)(a) ifthe height is below or approaching a value below the target range,providing the glass material at the location with energy in a greateramount, or (b) if the height is above or approaching a value above thetarget range, providing the glass material at the location with energyin a lesser amount, and (5) repeating steps (3) and (4) as needed tobring the height within the target range. According to another aspect ofpresent invention, methods and devices for automating this process arealso disclosed.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of certain aspects of a method according to thepresent invention;

FIG. 2 is a diagrammatic cross-sectional view of a glass surface beingtextured by electromagnetic radiation;

FIG. 3 is a diagrammatic cross-sectional view of a glass surface beingtextured by a surface-disposed energy concentrating element;

FIG. 4 is a diagrammatic cross-sectional view of a glass surface beingtextured by a probe tip;

FIG. 5 is a schematic diagram of a system or device for carrying out andautomating the method of the present invention;

FIG. 6 is a graph of experimental results of glass bump height inmicrometers as a function of dose energy in Joules of a laser pulse;

FIG. 7 is another graph of experimental results of glass bump height inmicrometers as a function of dose energy in Joules of a laser pulse;

FIG. 8 is a graph of the dose energies and resulting feature heights formultiple laser pulses raising a feature to 70 micrometers±100 nanometersaccording to the methods of the present invention;

FIG. 9 is a graph of the dose energies and resulting feature heights formultiple laser pulses raising a feature to 40 micrometers±100 nanometersaccording to the methods of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, example of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.

One embodiment of the method or process of the present invention isillustrated in the flow diagram of FIG. 1. This method allows theforming, on the surface of a glass material, of a raised feature ormultiple such features having a height within a target range. Suchraised features may include simple bumps, but also ridges and allvariety of more complex surface features resulting from combinations ofthese.

As may be seen in FIG. 1, the method 10 of the present inventiongenerally includes a step 1 of providing a glass material having asurface followed by a step 2 of applying a local energy dose, at alocation at or below the surface, with an amount of energy causing alocal expansion of the glass material so as to raise a feature on thesurface. Next, in a step 3, the height of the raised feature is measuredor detected, and optionally, if continuous energy dosing is used, theheight being approached is extrapolated. In a step 4, the measured ordetected or extrapolated height is compared to the target range asrepresented by the decision diamonds 12 and 14. If the current height,or the height being approached, is below the target range then the glassmaterial is provided with energy in a greater amount, as represented inpart a of step 4. If the current height, or the height being approached,is above the target range then the glass material is provided withenergy in a lesser amount, as represented in part b of step 4. As afinal step in the form of a repeat loop 5, steps 3 and 4 are repeated asneeded to bring the height within the target range.

The presently preferred means of supplying the energy used in the methodof FIG. 1 is shown in FIG. 2. In FIG. 2, a glass material 16 is shownbeing irradiated on a surface 20 thereof by radiation 18. The radiationis desirably from a laser beam or other electromagnetic source capableof producing an irradiated spot size on the order of 0.2-0.5millimeters. A focused or unfocused laser may be used, as may othersufficiently high intensity sources, whether coherent or not, if theyare focused and/or masked down to a sufficiently small spot size.Frequencies other than visible and infrared, such as microwave, maypotentially be of use. What is generally required is a sufficientlysmall spot size, together with sufficiently high power, and sufficientlyabsorptive glass material, such that an amount of energy is deposited ina small enough volume 24, so that a bump or other surface feature 22 israised and stays in place when the radiation is removed. Some care mustbe taken to appropriately match the absorption of the glass with thewavelength of radiation used. Highest absorption is not alwayspreferred, however, as deeper penetration of the radiation, with aconsequently deeper heating zone, tends to allow greater featureheights.

One alternative method of providing the energy used in the method ofFIG. 1 is shown in FIG. 3. In FIG. 3, a surface energy concentrator inthe form of a heating element 26 is positioned on the surface 20, andsupplied with energy, such as an electrical current from surface leads28 and bonded wires 30.

As another alternative method of providing the energy of the method ofFIG. 1 is shown in FIG. 4. In FIG. 4, an energy delivering probe in theform of a vibrating or rotating friction probe 90 heats the surface ofthe glass material 16.

According to one embodiment of the method of the present invention, thesteps shown in FIG. 1 are performed continuously, that is, theapplications of energy in steps 2 and 4 of FIG. 1 need not be discreteevents, but energy may be applied essentially continuously until aheight within a given target range is reached. Thus, in this embodiment,providing the glass material locally, at a location at or below thesurface, with an amount of energy, and providing the glass material withenergy in a greater amount, and providing the glass material with energyin a lesser amount, together comprise providing the glass material witha varying but continuous dose of energy.

An alternative is providing discrete doses of energy in steps 2 and 4 ofFIG. 1. In this embodiment, providing the glass material locally, at alocation at or below the surface, with an amount of energy, andproviding the glass material with energy in a greater amount, andproviding the glass material at the location with energy in a lesseramount, each comprise providing the glass material with a discrete doseof energy.

Of course these two alternatives may also be mixed such that discretedoses are sometimes used and continuous doses are sometimes used, ifdesired.

The methods of the present invention offer the ability to create raisedfeatures on the surface of a glass material having heights 10, 50, oreven 100-200 micrometers or greater. Bumps have even been produced asgreat as 250 micrometers in height. The method of the present inventionalso offers the ability to reliably achieve heights within target rangesas narrow as plus or minus 500, 200, and even 100 nanometers (nm).Producing features of 100 micrometers height to within ±100 nanometersrepresents a maximum variation in height of only one-half of onepercent.

As another aspect of the present invention, the method of claim 1 may beautomated, if desired. An example of a system 110 for automaticallysurface-texturing an article of glass material is shown in FIG. 5. Anx-y moveable stage device 40 includes a moveable stage 42 upon which anarticle of glass material 16 is placed. A controller 70, which may beanything from one or more items of dedicated circuitry or smallmicrocontrollers, up to a dedicated computer or a portion of a factorycontrol system, includes storage for, or has access to, informationrelating to one or more glass material's behavior under influence of oneor more types of energy, desirably laser energy as the presentlypreferred embodiment. The controller 70 also stores or has access to theraised feature or pattern of raised features to be formed. Thecontroller 70 uses the information, such as by a software or hardwareestimating algorithm, one or more look-up tables, or suitablesubstitutes therefor, to choose the initial energy and irradiation timebased on the target range. Generally, that amount of energy which ismost likely to achieve a feature height in the center of the targetrange is selected, although particular glass materials may call foraiming initially to the high or low side of center, if the target iseasier to approach from a particular side for a particular material or aparticular feature height. The controller also signals the stage device40 to position the stage 42 and glass material 16 so as to create thedesired feature at the desired location on the surface of material 16.

When the glass material is in the desired position, controller 70signals a laser device 50 to impart the chosen amount of energy via thebeam 18. Energies on the order of 1-10 Joules delivered in a time periodon the order of 0.1 to 2 seconds are believed generally appropriate,although times as long as 5 or 10 seconds have also succeeded intesting. As described above, the localized energy input causes theraising a surface feature. If discrete energy doses are used, the raisedportion becomes fixed in its raised state, very soon after theirradiation of the glass material 16 ends.

Whether discrete or continuous energy doses are used, the feature heightis then measured by a measuring device 60, such as an opticalprofilometer using a scanning measuring beam 62. For facilitating thismeasurement in the case of discrete energy doses, stage device 40 maymove the state 42 to the position shown in dashed outline in the figure.Alternatively, the measuring device may be positioned closely to, or mayeven be incorporated into, the optical system 52 of the laser device 50,as shown by the alternate measurement beam 63, or may be otherwisedirected toward the glass material in its first position, so that nomovement of the stage 42 is necessary. The optical system 52 of thelaser device 50 may even include beam steering capability, such that nomoveable stage 42 or moveable stage device 40 is required, even forformation of complex raised features, in automated system 110. In theabsence of more typical beam steering, the laser itself 10 or relevant aportion thereof may be moveable on mounting structure 80, as may be themeasuring device 60, such that even without beam steering, no moveablestage need be used. Use of a measurement system that operatesconcurrently with the irradiation beam 18 allows for use of continuousenergy doses to more quickly reach targeted ranges.

After determining whether the measured height is above or below target,a new energy amount is selected by the controller, in accord with themethod of FIG. 1, and the steps of irradiating and measuring arerepeated. It is preferred that the time of irradiation is kept the same,while the dose is varied. Where continuous energy doses are used, thecontroller is preferably programmed to take account of the growth trendsof the raised features as they are raised, such that not just theheight, but the height over time of the raised features is measured andrecorded or reflected within the controller's memory functions, suchthat the controller functions to extrapolate the final height beingapproached with a given dose energy. In the continuous dose embodiment,if the height is approaching a value below the target range, then theglass material is provided with energy in a greater amount, and if theheight is approaching a value above the target range, then the glassmaterial is provided with energy in a lesser amount.

EXPERIMENTAL

Glass compositions for which reasonably tall bumps have been achieved ata wavelength of 810 nm, and for composition 3 also for 1550 nm, arelisted in Table I below. The 1550 nm wavelength is desirable in order tofabricate bumps on glass that is covered with substrate like silicon,which is transparent at that wavelength. This is a principal wavelengthproduced by a 1.5-μm erbium fiber laser. Using this form of laser, thecapability to both increase and decrease bump heights has beendemonstrated.

TABLE I Composition Number 1 2 3 Oxides, SiO2 79.84 78.84 78.34Composition B2O3 10.56 10.56 10.56 (Mol %) Al2O3 1.21 1.21 1.21 Na2O5.38 5.38 5.38 Fe2O3 1 0 1.5 TiO2 2 2 3 K2O 0 0 0 CuO 0 0 0 CeO2 0 2 0Optical @ 810 nm 1.67 0.07 4.15 density in @ 1550 nm 0.72 — 2.73 log₁₀,@1 mm thickness Max. bump @ 810 nm 111/9.7 196/27.3   70/6.7 height, in@ 1550 nm — — 250/25 um, @ pulse energy, in J.

That bump or other feature height can be predicted reasonably well, as afunction of laser pulse energy dose, is shown by the experimentalresults graphed in FIGS. 6 and 7. FIG. 6 shows bump heights inmicrometers as a function of dose energy of a one-second laser pulse inJoules. The laser employed was an erbium-doped fiber laser at 1550 nmwavelength, and the glass composition was composition 3 of Table Iabove, with several different samples tested as shown by the variousgraph symbols. As may be seen from the figure, an essentially linearrelationship was revealed, with small variation. FIG. 7 shows theanother result for the relationship between the dose energy of aninitial one second laser pulse, in Joules on the x axis and bump heightin micrometers The light trace is one sample, and the dark trace anothersample of the same material used in the tests of FIG. 6. A 1550 Laseroutput is also used. FIG. 7 shows and extremely linear relationship upto about 10 Joules, above which the initial height is not so great. Itis presently preferred to stay within the initial linear portion of thecurve of FIG. 7. Data like that shown in FIGS. 6 and 7 are clearlyuseful to automate the selection of the initial pulse energy.

The ability to both increase and decrease the height of bumps or otherfeatures is critical to reaching height values within a narrow targetrange. In the previous practice, with no way to easily or reliablydecrease the height of a bump that is too high, an extremely uniformcontrol of the energy source (laser or other) is required, along withextreme uniformity of the glass material itself, so that heights withinnarrow target ranges may be reliably obtained. Such high uniformity ofglass material and such tight control of laser power are difficult.

In contrast, in accordance with the present invention, the height ofbumps or other features is adjusted, either up or down, as needed. FIGS.8 and 9 show two experimental examples of the method of the presentinvention, applied to achieve bump heights of 30 μm and greater towithin a target range of ±100 nm. Discrete energy doses were used. Foreach does, numbered on the x axis, dose energy is plotted as a trianglein Joules against the left axis, while resulting feature height isplotted as a circle in micrometers against the right axis.

Example 1

It was determined to raise a bump to a height of 70 μm±100 nm on asurface of a glass material corresponding to composition 3 of Table I,using 1510 nm radiation from an erbium-doped fiber laser. Relying ondata like that in FIGS. 6 and 7, an initial dose energy of 4.25 wattswas selected. The laser output was then focused on or a little under theglass surface into a 0.2-0.4 mm spot as 4.25 watts was irradiated overone second, forming an initial bump.

After the initial bump is formed, its height is measured with a laserprofiler as shown in FIG. 4. The measurement revealed an achieved heightof 68.5 μm—somewhat short of the desired height, as shown in FIG. 8.Since the height attained differed from the target value in that it wasshort by 1.5 μm, the adjustment process requires applying a higherenergy pulse than that used in the first shot to increase the height. Ifthis initial bump had overshot the target, it would have to be reducedby employing a lower energy pulse that that employed in the first shot.

Continuing with this example to trim (grow) the bump up to the desiredheight, a second shot of 4.39 J was administered, raising the bumpheight to ˜69.5 μm—still 0.5 μm short of the target. A third 4.44 J shotwas administered and in this example the height actually went down. Thissometimes occurs when trimming due to variations in the linearity of theloser output power versus the setting. The energies listed are theprojected ones based on the pump settings. In testing the laserpulse-to-pulse instability was around +/−5%. Hence, another shot wasrequired. A 4.53 J pulse was administered which grew the bump to 70.1μm, which was within +/−100 nm from the goal. This also demonstrates theability of this process to take up some of the slack in the laserpulse-to-pulse instability. That is, a less precise laser with a +/−5%pulse-to-pulse instability can be used.

Example 2

A second example is represented by the data shown in FIG. 6, wherein thebump height target value was 40 μm. Again, looking at the data presentedin FIGS. 6 and 7 helps guide the selection of laser pulse energyadministered for the first shot. In this example a 2.72 Joule pulse wasselected. This exposure resulted in a taller bump than desired −40.9 μm.Since the glass was produced in a small batch size, cord(inhomogeneities) is often observed. Again, the ability of the inventiveprocess to tune bump heights up and down does not require high quality,homogeneous samples. Since the bump height was taller than desired, asubsequent dose of less energy than the first is required to trim thebump height down. A second pulse of 2.63 J trimmed the bump height downto ˜40.45 μm. Finally, a third shot of 2.54 J brought the bump height to39.9 μm, within the target height desired.

1. A method of forming, on the surface of a glass material, a raisedfeature having a height within a target range, the method comprising:(1) providing a glass material having a surface; (2) providing the glassmaterial locally, at a location at or below the surface, with an amountof energy causing local expansion of the glass material so as to raise afeature on the surface at the location; (3) detecting the height of theraised feature or the height over time of the raised feature; and (4)(a)if the height is below or approaching a value below the target range,providing the glass material at the location with energy in a greateramount, (b) if the height is above or approaching a value above thetarget range, providing the glass material at the location with energyin a lesser amount, (5) repeating steps (3) and (4) as needed to bringthe height within the target range.
 2. The method according to claim 1wherein the height is at least 10 μm and the target range is equal to orless than ±500 nm of the height.
 3. The method according to claim 1wherein the target range is equal to or less than ±200 nm of the height.4. The method according to claim 1 wherein the target range is equal toor less than ±100 nm of the height.
 5. The method according to claim 1wherein the height is at least 30 μm.
 6. The method according to claim 1wherein the height is at least 80 μm.
 7. The method according to claim 1wherein the dose of energy is supplied by one or more of:electromagnetic radiation and friction.
 8. The method according claim 1further comprising the step of automatically performing steps (2)-(5).9. The method according to claim 1 wherein (1) providing the glassmaterial locally, at a location at or below the surface, with an amountof energy, and providing the glass material at the location with energyin a greater amount, and providing the glass material at the locationwith energy in a lesser amount, together comprise providing the glassmaterial with a varying but continuous dose of energy; or (2) providingthe glass material locally, at a location at or below the surface, withan amount of energy, and providing the glass material at the locationwith energy in a greater amount, and providing the glass material at thelocation with energy in a lesser amount, each comprise providing theglass material with a discrete dose of energy.
 10. The method accordingto claim 1 wherein providing the glass material with energy in a greateramount increases the height and providing the glass material with energyin a lesser amount decreases the height.
 11. The method according toclaim 1 comprising applying steps (4a) and (4b).